The Study Of Solid Oxide Fuel Cell Electrode Surface Of Cu-CeO₂ And Ni-CeO₂

Graduate dissertation is a graduate student in research results of concentrated reflection,represents the level of the graduate research work,is also the main basis of application and corresponding degree granted.Solid oxide fuel cell is an environmentally friendly electrochemical device that can efficiently change the form of power source.In the circumstances of IT,SOFC is a full solid state power device,which would transfer chemical energy stored inside the fuel into electricity.Although for experiments,the field of SOFC has been widely studied and developed,there are little studies about SOFC anode material on the atomic scale about its reaction mechanism.This paper will combine DFT and experiments,comprehensively study the reaction mechanism of H2 on the surface of Cu/CeO2(111)and Ni/CeO2(111).The first chapter will mainly discuss the development history of SOFC,briefly introduce the working mechanism and relevant concepts about O-SOFC.Then,the development of DFT and the theoretical basis of the utilization of First Principles will be mentioned.Thirdly,this paper will talk about the purpose of research and introduction of relevant contents.In the second chapter,we studied Cu-CeO2 system as anode materials.Because,by now,there are no clear description of the oxidation reaction of H2 on the surface of Cu/Ce02(111),it is highly valued to study this system with H2 as fuel gas.The calculation results of DFT show that Cu cluster on the surface of CeO2 could restrict the formation of oxygen vacancy on CeO2 surface,and also increase the catalytic activity of anode reaction,decrease the energy barrier of oxidation reaction of H2 on CeO2 system.There are two possible reaction paths of H2 on Cu-CeO2 surface,one is TPB Pathway reaction process,while the other is H-Spillover Pathway.The former has the smaller energy barrier,and its highest energy barrier is 0.836 eV,while the highest energy barrier of H,oxidation reaction on the stoichiometric Cu-CeO2(111)is 2.399 eV.Experimentally,H2-Temperature Programmed Reduction(H2-TPR)shows that Cu metal could reduce the reaction temperature of oxidation reaction within Cu-CeO2 system,increase the amount of reduced CeO2.Moreover,we compared this with ECR experiments,and found that nanoparticles of Cu could notably enhance the reaction velocity,because the oxygen surface exchange coefficient of pure CeO2 sample is 1.012×10-5 cm s-1,while that of Cu nanoparticle deposited on the CeO2 sample is 12.180×10-5 cm s-1.This result is compatible with the calculations of DFT.In the third chapter,we studied Ni-CeO2 system as anode material.Similarly,we also combined experiments and DFT calculations in order to study Ni-CeO2 system.Theoretical calculation focus on understanding the H2 oxidation reaction on Ni-CeO2 surface.Our study found that the reaction of H2 on the Ni-CeO2 surface could be categorized into H-Spillover Pathway,Molecule Pathway and O-Spillover Pathway.Among these three pathways,H-Spillover Pathway has the lowest energy barrier,while the whole O-Spillover Pathway reaction process is endothermic,which is incompatible with the fact that the reaction on the anode of SOFC is exothermic.In addition,the existence of Ni cluster reduces the energy barrier related to hydrogen oxidation processes of the adsorption-dissociation and surface oxygen evolution to H2O.Electrical conducting relaxation measurements exhibit shorter re-equilibrium time for Ni-CeO2,suggesting faster surface reaction processes.Temperature programmed desorption results prove that H2 molecules are more probably favorable adsorbed on Ni-CeO2 composite than CeO2.And AC impedance tests verify that the hydrogen electrochemical oxidation process,which corresponds to the process of surface oxygen evolution to H2O in DFT calculation,is greatly accelerated at the Ni-CeO2-gas three-phase boundaries.The DFT calculations and experiments results agree well and demonstrate that the adsorption-dissociation and surface oxygen evolution to H2O processes are strongly enhanced by the synergistic catalytic effects of Ni-Ceria in our H-spillover elementary reaction pathway.Finally,the forth chapter concluded the work of this thesis,at the same time some limitations and deficiencies are pointed out.